1. Field of the Invention
The present invention relates to semiconductor packages. More particularly, the present invention relates to semiconductor packages capable of incorporating radio frequency shielding.
2. Discussion of the Related Art
Modem electronic devices, for example cellular phones and pagers, require a seamless integration of analog and digital subsystems. Furthermore, premiums are often placed on small size, complexity, and high performance. Thus, sensitive analog circuits frequently need to be placed very close to high-speed digital systems.
High-speed digital systems can switch more then one hundred million times a second. At such switching speeds, switching currents tend to be high. Thus, such high-speed digital systems can radiate energy (noise) that interferes with sensitive analog circuits. Interference usually takes the form of signal crosstalk. While faraday shielding has been widely used to protect sensitive analog circuits from interference, the traditional faraday shields tend to be expensive. Furthermore, their implementation must be undertaken with great foresight to determine where to install the shields, and with great care to actually protect the analog circuits. Moreover, the traditional faraday shield is not particularly flexible.
Traditionally, semiconductor devices are packaged in semiconductor packages having external leads for soldering, or otherwise connecting, to a printed circuit board. For example, dual in-line packages (DIP) and surface mount leadless chip packages have been widely used. In such packages a semiconductor die is encapsulated in ceramic or plastic. FIGS. 1A-1D illustrate a typical prior art semiconductor device. Referring now to FIG. 1A, the prior art semiconductor device includes a lead frame 200 that is usually stamped out of a metal strip. The lead frame includes a plurality of leads 202 held together by connectors 204 that extend between rails 206. The lead frame 200 further includes a mounting pad 208. Referring now to FIG. 1B, which shows a cut-away view along lines A—A of FIG. 1A after a semiconductor die (beneficially an integrated circuit) 210 is mounted on the mounting pad 208, bonding conductors or wires 212 extend from exposed electrical contacts 214 on the semiconductor die 210 to the leads 202. Typically the bonding conductors 212 are welded to the exposed electrical contacts 214 and to the electrical pads of the leads 202. Next, as shown in FIG. 1C, the lead frame 200, the semiconductor die 210, and the bonding conductors 212 are then encapsulated. Finally, as shown in FIG. 1D, the leads 202 are then cut and formed as required to complete the semiconductor device 220. While not specifically discussed, the rails 206 and the connectors 204 are separated from the pad 208 and the leads 202 at some time during assembly. The leads 202 enable electrical signals to travel to and from the semiconductor die to the external environment.
While prior art semiconductor packages have been successful, they are not without problems. First, as semiconductor devices are mounted closer and closer together, the problem of cross-talk increases. This is a significant problem with analog circuits that have high impedance levels since they are particularly sensitive to crosstalk. Prior art semiconductor packages usually do not provide electrical and electromagnetic isolation of their components. Furthermore, prior art semiconductor packages can be inconvenient and expensive because they require semiconductor manufacturers to not only have semiconductor fabrication equipment on site, but also both wire bonding and encapsulation equipment.
Therefore, a semiconductor package capable of providing electrical and electromagnetic isolation of a component mounted therein would be beneficial. Even more beneficial would be a semiconductor package that enables dense packaging of semiconductor components, together with electrical and electromagnetic isolation. Even more beneficial would be a low cost semiconductor package that enables dense packaging together with electrical and electromagnetic isolation of semiconductor components.
Also advantageous would be a semiconductor package that does not require on-site encapsulation of the semiconductor die. Even more beneficial would be a prefabricated semiconductor package.